Various types of combustion may be used in an internal combustion engine. For example, spark ignition (SI) of a homogenous mixture during the expansion stroke is one example method. This method relies on a timed spark from a sparking plug in order to achieve ignition within the combustion chamber of an air and fuel mixture. Another type of combustion may be referred to as homogeneous charge compression ignition (HCCI), which occurs when the temperature of the combustion chamber exceeds an autoignition temperature for the specific fuel resulting in autoignition. HCCI can be used to provide greater fuel efficiency and reduced NOx production under some conditions.
In some cases it may be desirable to enable the combustion cylinders of the engine to operate either in SI mode or in HCCI mode, and from time to time during operation, switch from one mode to the other, so as to obtain the benefits associated with the different combustion modes. The benefits obtained by mode switching may be somewhat offset, however, by temporary performance and/or efficiency losses occurring as a result of transitioning the combustion mode for all of the cylinders. The presence of SI and HCCI combustion modes also presents aftertreatment issues, due to the significant differences in HCCI and SI combustion.
Thus, in one approach, the above issues may be addressed by an internal combustion engine, comprising: (a) a gasoline fuel injection system; (b) multiple combustion cylinders coupled with the gasoline fuel injection system and configured to receive gasoline from the gasoline fuel injection system, where the combustion cylinders are each further configured to operate selectively in either a spark ignition mode or in a compression ignition mode in which spark ignition is not employed; and (c) an electronic engine controller configured to allocate the combustion cylinders into a first group which is operated in the spark ignition mode, and a second group which is operated in the compression ignition mode, and where such allocation is dynamic such that the number of cylinders operating in each ignition mode is variable and changeable over time during operation of the internal combustion engine. In this way, multiple combustion modes may be flexibly and dynamically deployed in order to obtain an improved mix of advantages of the available combustion modes while minimizing the disadvantages associated with fixed combustion mode allocations and full cylinder set mode transitions.